1. Field of the Invention
This invention relates to a virtual storage system control apparatus, a virtual storage system control program and a virtual storage system control method for collectively controlling a plurality of virtual storage systems.
2. Description of the Related Art
Techniques for combining one or more than one storage devices or one or more than one resultant storage regions produced by dividing the storage regions of one or more than one storage devices so as to make it externally appear a single storage device are known. Such a virtual storage device is referred to as virtual volume or logical volume. The storage system that is supporting a virtual volume is referred to as virtual storage system. A virtual storage system provides an advantage of being capable of creating a virtual volume of a size that exceeds the physical limitations of a storage device.
The quantity of data stored in a storage system has been and being increasing in recent years. As the quantity of data increases, the storage system provided in advance may fall into a capacity shortage. Several methods are available to cope with such a capacity shortage.
Firstly, there is a method of preparing a new storage system having a large data storage capacity and replacing the existing storage system with the new one after moving all the data to the new one.
Secondly, there is a method of adding a node having one or more than one storage devices to consequently increase the available data storage capacity.
Thirdly, there is a method of adding a new storage system and assigning new volume or volumes to the added new storage system without blocking accesses to the existing volume or volumes.
Patent Document 1 (Jpn. Pat. Appln. Laid-Open Publication No. 2004-246770) is known as a document that describes the prior art relating to the present invention. With the data transfer method described in the patent document, a special relay device defines the cause that triggers the transfer of a virtual volume and the destination of the transfer. Then, it actually carries out the transfer and replaces the logical unit name after the completion of the transfer. The I/O processes during the transfer is managed by an applicable table. The described method is intended to concentrate the effective storage regions being controlled by the special relay device to nodes, the number of which is made as small as possible.
However, with the above-described first method, there arises a problem of how to provide services during the replacing operation and the preparatory operation for the replacement. With the above-described second method, various management problems arise in the virtual storage system as the number of storage devices and that of nodes increase. Finally, while it is possible to increase the capacity of the storage system without blocking accesses to the original volume or volumes with the above-described second and third methods, the services being provided have to be suspended when transferring from the original volume or volumes to the new volume or volumes.
There is a demand for moving one or more than one virtual volumes to a virtual storage system formed with one or more than one new nodes from a virtual storage system formed with one or more than one old nodes.
For example, if the storage node or nodes and the storage device or devices of an original virtual storage system have become obsolete with time, it will be possible to raise the level of response to accesses and the reliability of the overall system by moving virtual volumes to a new virtual storage system formed by using one or more than one storage nodes and one or more than one storage devices.
There is also a demand for moving one or more than one virtual volumes in order to exploit the new characteristic features of a newly added virtual storage system without suspending the services being provided. Such a demand may arise when a new virtual storage system is adapted to support encryption but a currently operating virtual storage system is not adapted to support encryption and data need to be encrypted for one or more than one virtual volumes having data same as those of the currently operating one or more than one virtual volumes, whichever appropriate and when a new virtual storage system is adapted to introduce check codes on a block by block basis and supports improvements of data security but a currently operating virtual storage system is not adapted to introduce check codes and cannot meet the demand for improving data security.
To the contrary, there is a demand for moving one or more than one virtual volumes in the opposite direction in order to improve the responsiveness to data accesses when the operating policy of the existing virtual storage system is replaced so that it is no longer necessary to improve the level of encryption and that of data security.
While the technique of Patent Document 1 can move data without interrupting services, the destination of move of the data cannot be beyond the above-described special relay device. Then, when the storage regions under a relay device become full and data need to be moved to the storages under some other relay device, it is necessary to suspend the services being provided and install additional storage regions.